We have prepared hybrids containing an alkylporphyrin covalently embedded in oligodeoxynucleotides via oxypropyl linkers to the phosphate groups of the backbone. These have allowed us to study interactions between a porphyrin similar in structure to common cofactors; found in nature and DNA. (Previous work in this field has almost exclusively been performed with xenobiotic meso-tetraarylporphyrins). A series of NMR spectra at different temperatures were recorded of the sequence 5'-CGCGCCTTC-P-CATTGCGG-3', where -P- denotes the porphyrin, complexed with a complementary DNA strand bearing a thymidine residue at the site facing the porphyrin. This duplex had been selected as the most stable among a number of different complexes. The spectra acquired on the FBML's 500 MHz spectrometer have allowed us to derive qualitative structural information about the porphyrin-DNA interactions. Together with other spectroscopic and footprinting data, the temperature-dependent NMR data have allowed us to propose herniintercalation of the macrocycle as the most likely structural consequence of the porphyrin-DNA interactions.